Thin sheet, film, and the like



Nov. 30, 1943. L. ECKLER 2,335,746

THIN SHEETS, FILMS, AND THE LIKE Filed March 1, 1939 :CPT'

VENTOR LEO/n25 ECKL ER B I d l1 ATTO /EYS Patented Nov. 30, 1943 THINSHEET,FILM,ANDTHELIKE Leopold Eckler, Binghamton, N. Y., assignor, by mesne assignments, to General Aniline & Film Corporation, New York, N. Y., a corporation oi Delaware Application March 1 1939, Serial No. 259,176

3 Claims. (Cl. 117-34).

My invention relates to thin sheets, films and the like, and to a process of obtaining them. The invention relates more particularly to the use of thickened portions near the edges of a strip of such films or sheets, which strip is to be wound on a suitable take-up reel.

For example, in the manufacture of photographic film base itis customary to apply the liquid film-forming material onto a casting surface from which the film base may later be stripped. The application of the film forming materialor solution may be made in any known manner, as byfiowing or spraying. It is also possible to force the fiuid through a slit or orifice into a suitable precipitating bath; The general process is well known to those skilled in the art and needs no ,detailed explanation here. As the film base is removed from the casting surface it may customarily pass over a suitable system of rollers or the like, which are adapted to apply additional thin layers (such as substratums and coating or protective layers) to the film in'known manner. Finally, the base is wound on a suitable take-up reel from which it may later be removed for any desired .purpose such as, for example, coating a light-sensitive emulsion thereon.

The known casting or film-forming processes,

- in spite of their extremely accurate adiustments I and carefully controlled conditions, nevertheless give rise to slight variations in thickness in the resulting films or sheets. These thickness variations, in turn, cause theformation of so-called beads or pressure marks after the films are wound on the take-up reel.. For instance, when there isa longitudinal thickened portion at some stretched slightly'in accommodating themselves to this unevenness, thereby giving rise to the subsequent pressure marks or beads mentioned.

above. 'Ihesepressuremarksorbeads, inturn, bring about the formation oi streaks in the light sensitive emulsion, if-such an emulsion is later coated thereon.

Furthermore, the films and formed often show a tendency to wrinkle or creasewhenovertherollersduringthe was these disadvantages and defects of the priorartinviemoneobiectofmyinventionis" toprovideameansoiting forthe unpoint in the sheet, this thickened portion, when even thicknesses in sheets and films which are to be wound on take-up reels or cores as described above. A further object is to provide a sheet or film which will not show pressure marks when rolled on itself. Another object is to provide a simple. and economical process for producing such sheets or films. A still further object is to provide a sheet or film on which a light sensitiveemulsion may be evenly coated, without the formation of streaks due to pressure marks. Additional objects will appear from the following specification, in which I shall describe a preferred form of my invention in such clear and concise terms as will be readily understood by those skilled in the art.

In the accompanying drawing forming a part .of this application, Fig. 1 is a greatly enlarged and exaggerated cross-sectional view of a film or sheet embodying one form of my invention; Fig.

2 is an enlarged and exaggerated cross-sectional view of a casting surface adapted to the production of such films or sheets; Fig. 3 is a reduced broken view of the full width of a sheet formed according to my process; Fig. 4 is an exaggerated broken sectional view showing the layers of film wound on a reel according to my invention; and Fig. 5 is an exaggerated broken perspective view of a slit used to form fihns by extrusion into .a precipitating bath.

Throughout my descriptionand claims I shall use the word film" to indicate any substantially broad and relatively thin and long strip of material which at some time in its handling may have topass over or be wound upon a suitable 'reel or core.

The film-forming material, in combination with suitable solvents, may be cast upon a continuous travelling casting surface It. This surface may or may not be provided with a further undercoating N such as is described, for example, in United States Patent No. 1,988,550 of Gladhorn and Eckler. In the preferred form of my invention Iiind it best to employ such an under-coating and toimpress thereinaserles of parallel shallow grooves running lengthwise of the casting surface near its edges. These grooves may be continuous or broken, and of. any desired number, spacing. and depth, but I have found that extremely satisractory results are obtained'by using four such grooves at each edge of. the casting surface, spacedabout of-an inch apart. These grooves maybeimpressedinthecasting'surfaoeorundercoatingin any desired manner-(as; for-example.

bytheuseofarotatingcylindrlcalmemberhavand partly by the type of material and solvents used, and must be greater than the greatest expected thickness variations in the central porsure marks which would cause streaks in the emulsion if'subsequent coatings were applied. The coated film may be safely left on the spools until such time as it is desired to apply additional coating layers or to cut and process the film in standard commercial sizes,

While I have described a seriesof parallel grooves in the casting,surface which give rise to parallel ridges on the film itself, it will be clear that the'resulting projections could be of any desired form orpattern. Also, in the production of sheets by forcing the film-forming solution through a narrow slit into a suitable precipitating tions of the sheet. I have found that under 'cer- I tain conditions the film-forming solution, although it at first levels off completely, later dries and shrinks above these depressions in the casting surface in such a Way as to produce smaller indentations, as at H, on the film itself opposite the projections or ridges ii. These recesses B2 are, however, somewhat shallower in depth than the thickness of the corresponding projections H. Thus, when the film is wound in layers on a reel or core W, as shown in Fig. 4, the parallel ridges, even though they may project somewhat into the corresponding recesses of the adjacent layer, will still tend to hold the successive layers slightly apart as at i9 and will leave the central portions of these successive layers substantially loose rather than in tight frictional contact with each other. Furthermore, the interlocking of these successive recesses and projections has proven extremely effective in preventing axial telescoping of the reels of film.

- While I do not wish to limit myself to any particular theory it is my belief that the thickened portions at the edges will separate the layers satisfactorily when such portions are spaced from each other as shown and comprise a small portion of the total surface near the edges.

In the photographic art it is customary to coat a light-sensitive emulsion on the film base obtained in the above manner. This emulsion layer causes a thickening of those portions of the film to which it is applied. Thus it might happen that this emulsion layer would more than offset the thickness advantages of my spaced projections. One way to offset this is to have projections thicker than the base plus the emulsion. Alternatively, my invention comprises the additional step of coating the emulsion over all or a part of the spaced projections as shown at 2B. -In this way, although the emulsionv will increase the thickness of the center portions of the film, it will correspondingly increase the thickness at the spaced projections. Thus the coated film may again be rolled on itself following the coatingoperation without giving rise to further-presbath, the slit 2! might be provided with spaced small notches22 (as indicated in Fig. 5) which would cause corresponding small parallel ridges on the resulting film.

In addition to the advantages in winding my improved film on a core or reel, I have found that such film, when the ,projectionstake the form of parallel ridges, has a desirable eittra stifiness which tends to prevent wrinkling "or creasing during the usual subbing and drying operations. Furthermore, such film 'tendst'o remain flatter and does not curl so much 'during'the coating operations. Thus there is less waste clue to defects, and the production of film is made more economical.

It is understood that my invention is not limited to the precise form shown herein since further variations and equivalents will be readily apparent to those skilled in the art. I therefore do not intend to be limited in the patent granted except as required by the prior art and the appended claim s.

With the foregoing description and illustrations in view, I claim the following:

1. A film adapted to be wound on a reel in overlying layers, said film having a plurality of parallel narrow ridges extending lengthwise on one side of the film near its edges and having a plurality of corresponding parallel recesses on the other side of the film directly opposite said ridges and shallower than the thickness of said ridges, whereby the film may be evenly wound on the reel without exerting tension on the central portions of said film and without substantial relative axial slippage between the overlying layers.

2. A film as in claim 1, said film being coated with a light-sensitive emulson which extends over a plurality of the spaced parallel ridges.

3. A film as in claim 1, said film being coated with a light-sensitive emulsion and said parallel ridges being of a size such that the thickness of the film itself at these points is greater than the greatest combined thickness of the film and emulsion at intermediate points. 1

, LEOPOLD ECKLER. 

